Why is sonny so surprised when Homer tells him how he feels about the mine?

Sonny is surprised when Homer expresses his feelings about the mine because he has always viewed it as a burdensome legacy, filled with danger and hardship. Homer's positive perspective contrasts sharply with Sonny's own disillusionment, highlighting the generational divide in their understanding of the family's history and the mine's significance. This revelation forces Sonny to reconsider his assumptions about his father's experiences and emotions, deepening their relationship.